Electrolyte system including alkali metal bis(fluorosulfonyl)imide and dimethyoxyethane for improving anodic stability of electrochemical cells

ABSTRACT

A highly-concentrated electrolyte system for an electrochemical cell is provided, along with methods of making the highly-concentrated electrolyte system. The electrolyte system includes a bound moiety having an ionization potential greater than an electron affinity and comprising one or more salts selected from the group consisting of: lithium bis(fluorosulfonyl)imide (LiFSI), sodium bis(fluorosulfonyl)imide (NaFSI), potassium bis(fluorosulfonyl)imide (KFSI), and combinations thereof bound to a solvent comprising dimethoxyethane (DME). The one or more salts have a concentration in the electrolyte system of greater than about 4M, and a molar ratio of the one or more salts to the dimethoxyethane (DME) is greater than or equal to about 1 to less than or equal to about 1.5. The one or more salts binds to the dimethoxyethane (DME) causing the electrolyte system to be substantially free of unbound dimethoxyethane (DME) and unbound bis(fluorosulfonyl)imide (FSI − ).

INTRODUCTION

This section provides background information related to the presentdisclosure which is not necessarily prior art.

The present disclosure pertains to a highly-concentrated ether-basedelectrolyte system of an electrochemical cell including a high-energycathode and a lithium-containing anode, along with methods of making thehighly-concentrated electrolyte system and electrochemical cellsincluding the highly-concentrated electrolyte system. The electrolytesystem includes a bound moiety including one or more salts associatedwith and/or bound to an ether-based solvent, wherein the one or moresalts have a concentration in the electrolyte system of greater thanabout 4M and a molar ratio of the one or more salts to the ether of theether-based solvent is greater than or equal to about 1 to less than orequal to about 1.5. The bound moiety of the electrolyte system improvesor supports the anodic stability of the electrochemical cell

By way of background, high-energy density, electrochemical cells, suchas lithium-ion batteries can be used in a variety of consumer productsand vehicles, such as Hybrid Electric Vehicles (HEVs) and ElectricVehicles (EVs). Typical lithium-ion batteries comprise a firstelectrode, a second electrode, an electrolyte material, and a separator.One electrode serves as a positive electrode or cathode and anotherserves as a negative electrode or anode. A stack of lithium-ion batterycells may be electrically connected to increase overall output.Conventional rechargeable lithium-ion batteries operate by reversiblypassing lithium ions back and forth between the negative electrode andthe positive electrode. A separator and an electrolyte are disposedbetween the negative and positive electrodes. The electrolyte issuitable for conducting lithium-ions and may be in solid (e.g., solidstate diffusion) or liquid form. Lithium-ions move from a cathode(positive electrode) to an anode (negative electrode) during charging ofthe battery, and in the opposite direction when discharging the battery.

Many different materials may be used to create components for alithium-ion battery. By way of non-limiting example, cathode materialsfor lithium-ion batteries typically comprise an electroactive materialwhich can be intercalated or alloyed with lithium ions, such aslithium-transition metal oxides or mixed oxides of the spinel type, forexample including spinel LiMn₂O₄, LiCoO₂, LiNiO₂, LiMn_(1.5)Ni_(0.5)O₄,LiNi_((1−x−y))Co_(x)M_(y)O₂ (where 0<x<1, y<1, and M may be Al, Mn, orthe like), or lithium iron phosphates. The electrolyte typicallycontains one or more lithium salts, which may be dissolved and ionizedin a non-aqueous solvent. Common negative electrode materials includelithium insertion materials or alloy host materials, like carbon-basedmaterials, such as lithium-graphite intercalation compounds, orlithium-silicon compounds, lithium-tin alloys, and lithium titanateLi_(4+x)Ti₅O₁₂, where 0≤x≤3, such as Li₄Ti₅O₁₂ (LTO).

The negative electrode may also be made of a lithium-containingmaterial, such as metallic lithium, so that the electrochemical cell isconsidered a lithium metal battery or cell. Metallic lithium for use inthe negative electrode of a rechargeable battery has various potentialadvantages, including having the highest theoretical capacity and lowestelectrochemical potential. Thus, batteries incorporating lithium metalanodes can have a higher energy density that can potentially doublestorage capacity, so that the battery may be half the size, but stilllast the same amount of time as other lithium ion batteries. Thus,lithium metal batteries are one of the most promising candidates forhigh energy storage systems. However, lithium metal batteries also havepotential downsides, including possibly exhibiting unreliable ordiminished performance and potential premature electrochemical cellfailure.

For example, side reactions may occur between the lithium metal andspecies in the adjacent electrolyte disposed between the positive andnegative electrodes promoting performance degradation with lithiumnegative electrodes, which can compromise coulombic efficiency andcycling lifetime of rechargeable lithium batteries. Accordingly, itwould be desirable to develop materials for use in high energylithium-ion batteries that reduce or suppress lithium metal sidereactions thereby similarly suppressing or minimizing effects resultingtherefrom.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In various aspects, the present disclosure provides a method ofpreparing an electrolyte system that enhances or optimizes an anodicstability of an electrochemical cell that may include a positiveelectrode and a negative electrode. The positive electrode may include apositive lithium-based electroactive material having a maximum potentialgreater than or equal to about 5V. The negative electrode may include anegative electroactive material that comprises lithium. The method mayinclude mixing one or more salts selected from the group consisting of:lithium bis(fluorosulfonyl)imide (LiFSI), sodiumbis(fluorosulfonyl)imide (NaFSI), potassium bis(fluorosulfonyl)imide(KFSI), and combinations thereof and a solvent comprisingdimethoxyethane (DME) to form a bound moiety. The bound moiety may havean ionization potential greater than an electron affinity to form anelectrolyte system that is substantially free of unbound dimethoxyethane(DME) and unbound bis(fluorosulfonyl)imide (FSI⁻). The one or more saltsmay have a concentration in the electrolyte system of greater than about4M. A molar ratio of the one or more salts to the dimethoxyethane (DME)may be greater than or equal to about 1 to less than or equal to about1.5.

In one aspect, the electrolyte system may have a dynamic viscosity ofless than about 100 centipoise (cP).

In one aspect, the electrochemical cell may have an energy density ofgreater than about 900 Wh/L.

In one aspect, the electrolyte system may include one or moreelectrolyte additives. The electrolyte additives may be selected fromthe group consisting of: organic silane electrolyte additives, boratebased electrolyte additives, and combinations thereof.

In one aspect, the one or more electrolyte additives may include anorganic silane electrolyte additive selected from the group consistingof: fluorinated methoxysilanes, fluorinated chlorosilanes, andcombinations thereof.

In one aspect, the electrolyte system may include one or moreelectrolyte additives selected from the group consisting of:3,3,3-trifluoropropylmethyldimethoxysilane,(3,3,3-trifluoropropyl)trimethoxysilane,1H,1H,2H,2H-perfluorooctylmethyldimethoxysilane,1H,1H,2H,2H-perfluorooctyltrimethoxysilane,1H,1H,2H,2H-perfluorooctyldimethylchlorosilane,1H,1H,2H,2H-perfluorooctylmethyldichlorosilane,(1H,1H,2H,2H-perfluoro-n-hexyl)methyldichlorosilane,1H,1H,2H,2H-perfluorooctyltrichlorosilane, and combinations thereof.

In one aspect, the positive lithium-based electroactive material mayinclude elemental sulfur or a sulfur-containing active material.

In one aspect, the positive lithium-based electroactive material may beselected from the group consisting of: nickel-manganese-cobalt 811(NMC811); nickel-manganese-cobalt 622 (NMC622); lithium cobalt oxide(LiCoO₂); lithium iron phosphate (LiFePO₄); high-energynickel-manganese-cobalt-oxide (HENMC) (e.g., over-lithiated layeredoxide cathode or lithium-rich NMC); lithium-manganese-nickel-oxide(LMNO); and combinations thereof.

In another variation, the present disclosure provides another method ofimproving or optimizing anodic stability of an electrochemical cell thatcycles lithium-ions. The method may include introducing an electrolytesystem into the electrochemical cell. The electrolyte system may includea bound moiety having an ionization potential greater than an electronaffinity. The electrolyte system may include one or more salts bound toa solvent. The electrolyte system may include one or more salts having aconcentration in the electrolyte system of greater than 4M. The one ormore salts may be selected from the group consisting of: lithiumbis(fluorosulfonyl)imide (LiFSI), sodium bis(fluorosulfonyl)imide(NaFSI), potassium bis(fluorosulfonyl)imide (KFSI), and combinationsthereof and the solvent may comprise dimethoxyethane (DME). A molarratio of the one or more salts to the dimethoxyethane (DME) may begreater than or equal to about 1 to less than or equal to about 1.5. Theelectrolyte system may be substantially free of unbound dimethoxyethane(DME) and unbound bis(fluorosulfonyl)imide (FSI⁻).

In one aspect, the electrochemical cell may include a positive electrodeand a negative electrode. The positive electrode may include a positivelithium-based electroactive material having a maximum potential greaterthan or equal to about 5V. The negative electrode may have a negativeelectrolyte material comprising lithium.

In one aspect, the electrolyte system may have a dynamic viscosity of100 centipoise (cP).

In one aspect, the electrochemical cell may have an energy density ofgreater than about 900 Wh/L.

In one aspect, the electrolyte system may include one or moreelectrolyte additives. The electrolyte additives may be selected fromthe group consisting of: organic silane electrolyte additives, boratebased electrolyte additives, and combinations thereof.

In another variation, the present disclosure provides an electrochemicalcell that cycles lithium-ions having improved or optimized anodicstability. The electrochemical cell may include a positive electrode, aseparator, a negative electrode, and an electrolyte system. The positiveelectrode may include a positive lithium-based electroactive materialand may have a maximum potential greater than or equal to about 5V. Thenegative electrode may include a negative electroactive materialincluding lithium. The electrolyte system may include a bound moietyhaving an ionization potential greater than an electron affinity and maycomprise one or more salts bound to a solvent. The one or more salts maybe selected from the group consisting of: lithiumbis(fluorosulfonyl)imide (LiFSI), sodium bis(fluorosulfonyl)imide(NaFSI), potassium bis(fluorosulfonyl)imide (KFSI), and combinationsthereof and the solvent may comprise dimethoxyethane (DME). The one ormore salts may have a concentration in the electrolyte system of greaterthan 4M. A molar ratio of the one or more salts to the dimethoxyethane(DME) may be greater than or equal to about 1 to less than or equal toabout 1.5. The electrolyte system may be substantially free of unbounddimethoxyethane (DME) and unbound bis(fluorosulfonyl)imide (FSI⁻).

In one aspect, the electrolyte system may have a dynamic viscosity of100 centipoise (cP).

In one aspect, the electrochemical cell may have an energy density ofgreater than about 900 Wh/L.

In one aspect, the electrolyte system may include one or moreelectrolyte additives. The electrolyte additives may be selected fromthe group consisting of: organic silane electrolyte additives, boratebased electrolyte additives, and combinations thereof.

In one aspect, the one or more electrolyte additives may include anorganic silane electrolyte additive selected from the group consistingof: fluorinated methoxysilanes, fluorinated chlorosilanes, andcombinations thereof.

In one aspect, the electrolyte system may include one or moreelectrolyte additives selected from the group consisting of:3,3,3-trifluoropropylmethyldimethoxysilane,(3,3,3-trifluoropropyl)trimethoxysilane,1H,1H,2H,2H-perfluorooctylmethyldimethoxysilane,1H,1H,2H,2H-perfluorooctyltrimethoxysilane,1H,1H,2H,2H-perfluorooctyldimethylchlorosilane,1H,1H,2H,2H-perfluorooctylmethyldichlorosilane,(1H,1H,2H,2H-perfluoro-n-hexyl)methyldichlorosilane,1H,1H,2H,2H-perfluorooctyltrichlorosilane, and combinations thereof.

In one aspect, the positive lithium-based electroactive material mayinclude elemental sulfur or a sulfur-containing active material.

In one aspect, the positive lithium-based electroactive material may beselected from the group consisting of: nickel-manganese-cobalt 811(NMC811); nickel-manganese-cobalt 622 (NMC622); lithium cobalt oxide(LiCoO₂); lithium iron phosphate (LiFePO₄); high-energynickel-manganese-cobalt-oxide (HENMC) (e.g., over-lithiated layeredoxide cathode or lithium-rich NMC); lithium-manganese-nickel-oxide(LMNO); and combinations thereof.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a schematic of an exemplary electrochemical battery cellincluding a lithium-containing negative electrode;

FIG. 2 shows an electrolyte system wherein one or more salts have aconcentration in the electrolyte system of about 5M;

FIG. 3 shows an electrolyte system wherein one or more salts have aconcentration in the electrolyte system of less than about 4M;

FIG. 4 is a graphical illustration of electron affinities and ionizationpotentials of comparative electrolyte systems; and

FIG. 5 is a graphical illustration of the capacity retention per cycleof example electrochemical cells.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific compositions, components, devices, and methods, to provide athorough understanding of embodiments of the present disclosure. It willbe apparent to those skilled in the art that specific details need notbe employed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, elements, compositions, steps, integers, operations, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof. Although the open-ended term “comprising,” is tobe understood as a non-restrictive term used to describe and claimvarious embodiments set forth herein, in certain aspects, the term mayalternatively be understood to instead be a more limiting andrestrictive term, such as “consisting of” or “consisting essentiallyof.” Thus, for any given embodiment reciting compositions, materials,components, elements, features, integers, operations, and/or processsteps, the present disclosure also specifically includes embodimentsconsisting of, or consisting essentially of, such recited compositions,materials, components, elements, features, integers, operations, and/orprocess steps. In the case of “consisting of,” the alternativeembodiment excludes any additional compositions, materials, components,elements, features, integers, operations, and/or process steps, while inthe case of “consisting essentially of,” any additional compositions,materials, components, elements, features, integers, operations, and/orprocess steps that materially affect the basic and novel characteristicsare excluded from such an embodiment, but any compositions, materials,components, elements, features, integers, operations, and/or processsteps that do not materially affect the basic and novel characteristicscan be included in the embodiment.

Any method steps, processes, and operations described herein are not tobe construed as necessarily requiring their performance in theparticular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed, unless otherwiseindicated.

When a component, element, or layer is referred to as being “on,”“engaged to,” “connected to,” or “coupled to” another element or layer,it may be directly on, engaged, connected or coupled to the othercomponent, element, or layer, or intervening elements or layers may bepresent. In contrast, when an element is referred to as being “directlyon,” “directly engaged to,” “directly connected to,” or “directlycoupled to” another element or layer, there may be no interveningelements or layers present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.). As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various steps, elements, components, regions, layers and/orsections, these steps, elements, components, regions, layers and/orsections should not be limited by these terms, unless otherwiseindicated. These terms may be only used to distinguish one step,element, component, region, layer or section from another step, element,component, region, layer or section. Terms such as “first,” “second,”and other numerical terms when used herein do not imply a sequence ororder unless clearly indicated by the context. Thus, a first step,element, component, region, layer or section discussed below could betermed a second step, element, component, region, layer or sectionwithout departing from the teachings of the example embodiments.

Spatially or temporally relative terms, such as “before,” “after,”“inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and thelike, may be used herein for ease of description to describe one elementor feature's relationship to another element(s) or feature(s) asillustrated in the figures. Spatially or temporally relative terms maybe intended to encompass different orientations of the device or systemin use or operation in addition to the orientation depicted in thefigures.

Throughout this disclosure, the numerical values represent approximatemeasures or limits to ranges to encompass minor deviations from thegiven values and embodiments having about the value mentioned as well asthose having exactly the value mentioned. Other than in the workingexamples provided at the end of the detailed description, all numericalvalues of parameters (e.g., of quantities or conditions) in thisspecification, including the appended claims, are to be understood asbeing modified in all instances by the term “about” whether or not“about” actually appears before the numerical value. “About” indicatesthat the stated numerical value allows some slight imprecision (withsome approach to exactness in the value; approximately or reasonablyclose to the value; nearly). If the imprecision provided by “about” isnot otherwise understood in the art with this ordinary meaning, then“about” as used herein indicates at least variations that may arise fromordinary methods of measuring and using such parameters. For example,“about” may comprise a variation of less than or equal to 5%, optionallyless than or equal to 4%, optionally less than or equal to 3%,optionally less than or equal to 2%, optionally less than or equal to1%, optionally less than or equal to 0.5%, and in certain aspects,optionally less than or equal to 0.1%.

In addition, disclosure of ranges includes disclosure of all values andfurther divided ranges within the entire range, including endpoints andsub-ranges given for the ranges.

Example embodiments will now be described more fully with reference tothe accompanying drawings.

The present technology pertains to improved electrochemical cells,especially lithium-ion or more particularly lithium-metal batteries,which may be used in vehicle applications. However, the presenttechnology may also be used in other electrochemical devices; especiallythose that comprise lithium, such as lithium-sulfur batteries. Thus, thediscussion of a lithium-ion battery herein is non-limiting.

An exemplary and schematic illustration of a battery 20 that cycleslithium ions is shown in FIG. 1. Battery 20 includes a negativeelectrode 22, a positive electrode 24, and a porous separator 26 (e.g.,a microporous or nanoporous polymeric separator) disposed between thetwo electrodes 22, 24. The porous separator 26 includes an electrolyte30, which may also be present in the negative electrode 22 and positiveelectrode 24. A negative electrode current collector 32 may bepositioned at or near the negative electrode 22, and a positiveelectrode current collector 34 may be positioned at or near the positiveelectrode 24. The negative electrode current collector 32 and positiveelectrode current collector 34 respectively collect and move freeelectrons to and from an external circuit 40. An interruptible externalcircuit 40 and load device 42 connects the negative electrode 22(through its current collector 32) and the positive electrode 24(through its current collector 34).

The porous separator 26 operates as both an electrical insulator and amechanical support, by being sandwiched between the negative electrode22 and the positive electrode 24 to prevent physical contact and thus,the occurrence of a short circuit. The porous separator 26, in additionto providing a physical barrier between the two electrodes 22, 24, canprovide a minimal resistance path for internal passage of lithium ions(and related anions) during cycling of the lithium ions to facilitatefunctioning of the battery 20. While in lithium-ion batteries, lithiumintercalates and/or alloys in the electrode active materials, in alithium sulfur battery, instead of intercalating or alloying, thelithium dissolves from the negative electrode and migrates to thepositive electrode where it reacts/plates during discharge, while duringcharging, lithium plates on the negative electrode.

The battery 20 can be charged or re-energized at any time by connectingan external power source to the battery 20 to reverse theelectrochemical reactions that occur during battery discharge. Theconnection of an external power source to the battery 20 compels theproduction of electrons and release of lithium ions from the positiveelectrode 25. The electrons, which flow back towards the negativeelectrode 22 through the external circuit 40, and the lithium ions,which are carried by the electrolyte 30 across the separator 26 backtowards the negative electrode 22, reunite at the negative electrode 22and replenish it with lithium for consumption during the next batterydischarge cycle. As such, each discharge and charge event is consideredto be a cycle, where lithium ions are cycled between the positiveelectrode 24 and negative electrode 22.

The external power source that may be used to charge the battery 20 mayvary depending on the size, construction, and particular end-use of thebattery 20. Some notable and exemplary external power sources include,but are not limited to, an AC wall outlet and a motor vehiclealternator. In many lithium-ion battery configurations, each of thenegative electrode current collector 32, negative electrode 22, theseparator 26, positive electrode 24, and positive electrode currentcollector 34 are prepared as relatively thin layers (for example, fromseveral microns to a millimeter or less in thickness) and assembled inlayers connected in electrical parallel arrangement to provide asuitable electrical energy and power package.

Furthermore, the battery 20 can include a variety of other componentsthat while not depicted here are nonetheless known to those of skill inthe art. For instance, the battery 20 may include a casing, gaskets,terminal caps, tabs, battery terminals, and any other conventionalcomponents or materials that may be situated within the battery 20,including between or around the negative electrode 22, the positiveelectrode 24, and/or the separator 26, by way of non-limiting example.As noted above, the size and shape of the battery 20 may vary dependingon the particular application for which it is designed. Battery-poweredvehicles and hand-held consumer electronic devices, for example, are twoexamples where the battery 20 would most likely be designed to differentsize, capacity, and power-output specifications. The battery 20 may alsobe connected in series or parallel with other similar lithium-ion cellsor batteries to produce a greater voltage output, energy, and power ifit is required by the load device 42.

Accordingly, the battery 20 can generate electric current to a loaddevice 42 that can be operatively connected to the external circuit 40.While the load device 42 may be any number of known electrically-powereddevices, a few specific examples of power-consuming load devices includean electric motor for a hybrid vehicle or an all-electric vehicle, alaptop computer, a tablet computer, a cellular phone, and cordless powertools or appliances, by way of non-limiting example. The load device 42may also be a power-generating apparatus that charges the battery 20 forpurposes of storing energy. In certain other variations, theelectrochemical cell may be a supercapacitor, such as a lithium-ionbased supercapacitor.

With renewed reference to FIG. 1, the porous separator 26 may include,in certain instances, a microporous polymeric separator including apolyolefin, by way of non-limiting example. The polyolefin may be ahomopolymer (derived from a single monomer constituent) or aheteropolymer (derived from more than one monomer constituent), whichmay be either linear or branched. If a heteropolymer is derived from twomonomer constituents, the polyolefin may assume any copolymer chainarrangement, including those of a block copolymer or a random copolymer.Similarly, if the polyolefin is a heteropolymer derived from more thantwo monomer constituents, it may likewise be a block copolymer or arandom copolymer. In certain aspects, the polyolefin may be polyethylene(PE), polypropylene (PP), or a blend of PE and PP, or multi-layeredstructured porous films of PE and/or PP. Commercially availablepolyolefin porous membranes 26 include CELGARD® 2500 (a monolayerpolypropylene separator) and CELGARD® 2320 (a trilayerpolypropylene/polyethylene/polypropylene separator) available fromCelgard LLC.

When the porous separator 26 is a microporous polymeric separator, itmay be a single layer or a multi-layer laminate, which may be fabricatedfrom either a dry or wet process. For example, in one embodiment, asingle layer of the polyolefin may form the entire microporous polymerseparator 26. In other aspects, the separator 26 may be a fibrousmembrane having an abundance of pores extending between the opposingsurfaces and may have a thickness of less than a millimeter, forexample. As another example, however, multiple discrete layers ofsimilar or dissimilar polyolefins may be assembled to form themicroporous polymer separator 26. Furthermore, the porous separator 26may be mixed with a ceramic material or its surface may be coated in aceramic material. For example, a ceramic coating may include alumina(Al₂O₃), silicon dioxide (SiO₂), or combinations thereof. Variousconventionally available polymers and commercial products for formingthe separator 26 are contemplated, as well as the many manufacturingmethods that may be employed to produce such a microporous polymerseparator 26.

In various aspects, the positive electrode 24 may be formed from alithium-based active material that can sufficiently undergo lithiumintercalation and deintercalation, alloying and dealloying, or platingand stripping, while functioning as the positive terminal of the battery20. The positive electrode 24 electroactive materials may include one ormore transition metals, such as manganese (Mn), nickel (Ni), cobalt(Co), chromium (Cr), iron (Fe), vanadium (V), and combinations thereof.Two exemplary common classes of known electroactive materials that canbe used to form the positive electrode 24 are lithium transition metaloxides with layered structure and lithium transition metal oxides withspinel phase.

For example, in certain instances, the positive electrode 24 may includea spinel-type transition metal oxide, like lithium manganese oxide(Li_((1+x))Mn_((2−x))O₄), where x is typically less than 0.15, includingLiMn₂O₄ (LMO) and lithium manganese nickel oxideLiMn_(1.5)Ni_(0.5)O₄(LMNO). In other instances, the positive electrode24 may include layered materials like lithium cobalt oxide (LiCoO₂),lithium nickel oxide (LiNiO₂), a lithium nickel manganese cobalt oxide(Li(Ni_(x)Mn_(y)Co_(z))O₂), where 0≤x≤1, 0≤y≤1, 0≤z≤1, and x+y+z=1,including LiMn_(0.33)Ni_(0.33)Co_(0.33)O₂, a lithium nickel cobalt metaloxide (LiNi_((1−x−y))Co_(x)M_(y)O₂), where 0<x<1, 0<y<1 and M may be Al,Mn, or the like. Other known lithium-transition metal compounds such aslithium iron phosphate (LiFePO₄) or lithium iron fluorophosphate(Li₂FePO₄F) can also be used. In certain aspects, the positive electrode24 may include an electroactive material that includes manganese, suchlithium manganese oxide (Li_((1+x))Mn_((2−x))O₄), a mixed lithiummanganese nickel oxide (LiMn_((2−x))Ni_(x)O₄), where 0≤x≤1, and/or alithium manganese nickel cobalt oxide (e.g.,LiMn_(1/3)Ni_(1/3)Co_(1/3)O₂). In a lithium-sulfur battery, positiveelectrodes may have elemental sulfur as the active material or asulfur-containing active material.

In certain variations, the electroactive material used to form thepositive electrode 24 may have a maximum potential of greater than orequal to about 4V, optionally greater than or equal to about 4.8V, andin certain aspects, optionally greater than or equal to about 5V. Forexample, in certain instances, the positive electrode 24 may include apositive lithium-based electroactive material selected from the groupconsisting of nickel-manganese-cobalt 811 (NMC811);nickel-manganese-cobalt 622 (NMC622); lithium cobalt oxide (LiCoO₂);lithium iron phosphate (LiFePO₄); high-energynickel-manganese-cobalt-oxide (HENMC) (e.g., over-lithiated layeredoxide cathode or lithium-rich NMC); lithium-manganese-nickel-oxide(LMNO); and combinations thereof.

In certain variations, the positive active materials may be intermingledwith an optional electrically conductive material and at least onepolymeric binder material to structurally fortify the lithium-basedactive material along with an optional electrically conductive particledistributed therein. For example, the active materials and optionalconductive materials may be slurry cast with such binders, likepolyvinylidene difluoride (PVdF), polytetrafluoroethylene (PTFE),ethylene propylene diene monomer (EPDM) rubber, or carboxymethoxylcellulose (CMC), a nitrile butadiene rubber (NBR), lithium polyacrylate(LiPAA), sodium polyacrylate (NaPAA), sodium alginate, lithium alginate.Electrically conductive materials may include graphite, carbon-basedmaterials, powdered nickel, metal particles, or a conductive polymer.Carbon-based materials may include by way of non-limiting exampleparticles of KETCHEN™ black, DENKA™ black, acetylene black, carbonblack, and the like. Examples of a conductive polymer includepolyaniline, polythiophene, polyacetylene, polypyrrole, and the like. Incertain aspects, mixtures of conductive materials may be used. Thepositive electrode current collector 34 may be formed from aluminum (Al)or any other appropriate electrically conductive material known to thoseof skill in the art.

In various aspects, the negative electrode 22 includes an electroactivematerial capable of functioning as a negative terminal of the battery20. The negative electrode 22 may thus include the electroactivematerial and optionally another electrically conductive material, aswell as one or more polymeric binder materials to structurally hold thelithium host material together. In various aspects, the electroactivematerial comprises lithium and may be lithium metal. In certainvariations, the negative electrode 22 is a film or layer formed oflithium metal or an alloy of lithium. As noted above, metallic lithiumfor use in the negative electrode (e.g., 22) of a rechargeable battery(e.g., 20) has various potential advantages, including having thehighest theoretical capacity (e.g., about 3860 mAh/g (LiC₆: 339 mAh/g;Li_(3.75)Si: 1860 mAh/g)) and lowest electrochemical potential. Further,batteries (e.g., 20) incorporating lithium metal anodes (e.g., 22) mayhave a higher energy density (e.g., greater than or equal to about 800Wh/L and 350 Wh/Kg) that can potentially double storage capacity.

In certain variations, the negative electrode 22 may optionally anotherelectrically conductive material, as well as one or more polymericbinder materials to structurally hold the lithium host materialtogether. By way of non-limiting example, the negative electrode 22 mayinclude an active material including lithium metal particles (e.g.,lithium foil) intermingled with a binder material selected from thegroup consisting of: polyvinylidene difluoride (PVdF),polytetrafluoroethylene (PTFE), ethylene propylene diene monomer (EPDM)rubber, or carboxymethoxyl cellulose (CMC), a nitrile butadiene rubber(NBR), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodiumalginate, lithium alginate, and combinations thereof. Suitableadditional electrically conductive materials may include carbon-basedmaterial or a conductive polymer. Carbon-based materials may include byway of non-limiting example, particles of KETCHEN™ black, DENKA™ black,acetylene black, carbon black, and the like. Examples of a conductivepolymer include polyaniline, polythiophene, polyacetylene, polypyrrole,and the like. In certain aspects, mixtures of conductive materials maybe used. The negative electrode current collector 32 may be formed fromcopper (Cu) or any other appropriate electrically conductive materialknown to those of skill in the art.

As noted, each of the separator 26, the negative electrode 22, and thepositive electrode 24 may include an electrolyte system 30, capable ofconducting lithium ions between the negative electrode 22 and thepositive electrode 24. The electrolyte system 30 may be a non-aqueousliquid electrolyte solution including a bound moiety. The bound moietymay comprise one or more salts associated with or bound to an organicsolvent or a mixture of organic solvents. In certain instances, the oneor more lithium salts may be selected from the group consisting of:lithium bis(fluorosulfonyl)imide (LiFSI), sodiumbis(fluorosulfonyl)imide (NaFSI), potassium bis(fluorosulfonyl)imide(KFSI), and combinations thereof and the solvent may comprise anether-based solvent. For example, the bound moiety of the electrolytesystem 30 may include one or more lithium salts selected from the groupconsisting of: lithium bis(fluorosulfonyl)imide (LiFSI), sodiumbis(fluorosulfonyl)imide (NaFSI), potassium bis(fluorosulfonyl)imide(KFSI), and combinations thereof and a solvent comprisingdimethoxyethane (DME). A molar ratio of the one or more salts to thedimethoxyethane (DME) may be greater than or equal to about 1 to lessthan or equal to about 1.5M. The one or more salts may have aconcentration in the electrolyte system 30 of greater than 4M,optionally greater than or equal to about 4.5M, and in certain aspects,optionally greater than or equal to about 5M.

In various aspects, the electrolyte system 30 has an ionizationpotential greater than an electron affinity. For example, theelectrolyte system 30 may have a calculated electron affinity less thanor equal to about 1.5 eV; and a calculated ionization potential greaterthan or equal to about 10 eV. In certain instances, the electrolytesystem 30 may have a dynamic viscosity of less than about 100 centipoise(cP), and a battery 20 including electrolyte system 30 may have anenergy density of greater than about 900 Wh/L.

In various aspects, bound moiety of the electrolyte system 30 improvesor supports the anodic stability of the battery 20 by suppressing orminimizing side reactions that may occur when the solvent and/or saltsare unbound or free species in the electrolyte system 30 that may reactwith the lithium (Li) metal of the negative electrode 22. Side reactionsmay compromise coulombic efficiency and cycling lifetime of rechargeablebatteries by consuming the lithium (Li) metal and electrolyte.Ether-based electrolyte systems generally experience good compatibilitywith lithium (Li) metal. For example, dimethoxyethane (DME) has anelectron affinity of about 1.5 eV, which makes it generally compatiblewith lithium (Li) metal. However, ether-based electrolyte systems havinglow concentrations (less than about 4M, and in certain aspects, lessthan about 3M) may experience low anodic stability and may be suitableonly for use with low voltage cathodes, such as Li—S, Li—MoS₂, andLiFePO₄ batteries wherein the cathodes have maximum potentials of lessthan about 3.7V. For example, dimethoxyethane (DME) has an ionizationpotential of less than about 7.2 eV, which allows for easy oxidization(loss of electrons) at the cathode.

Providing electrolyte systems 30 having higher concentrations of salts(e.g., greater than 4M, optionally greater than or equal to about 4.5M,and in certain aspects, optionally greater than or equal to about 5M)may enhance anodic stability and allow for the use of higher voltagecathodes (e.g., cathodes having a maximum potential greater than orequal to about 4V, optionally greater than or equal to about 4.8V, andin certain aspects, optionally greater than or equal to about 5V) atleast in part because an increase salt concentration increases theionization potential of dimethoxyethane (DME) to greater than or equalto about 10 eV. Electrolyte system 30, having an increased saltconcentration and a molar ratio of the one or more salts to thedimethoxyethane (DME) is greater than or equal to about 1 to less thanor equal to about 1.5, may thus be substantially free of such free orunbound compounds that promote such side reactions (e.g., oxidization atthe cathode). Electrolyte system 30 may comprise less than or equal toabout 0.5% by weight, optionally less than or equal to about 0.25% byweight, optionally less than or equal to about 0.1% by weight, and incertain aspects, 0% by weight of the free or unbound undesired species,like unbound salt(s) or unbound solvent(s) (e.g., dimethoxyethane(DME)).

In certain instances, the electrolyte system 30 may include one or moreelectrolyte additives. For example, the electrolyte system 30 mayinclude one or more electrolyte additives selected from the groupconsisting of: organic silane electrolyte additives, borate basedelectrolyte additives, and combinations thereof. The organic silaneelectrolyte additive may be selected from the group consisting offluorinated methoxysilanes, fluorinated chlorosilanes, and combinationsthereof. In certain instances, the electrolyte system 30 may include oneor more electrolyte additives may be selected from the group consistingof: 3,3,3-trifluoropropylmethyldimethoxysilane,(3,3,3-trifluoropropyl)trimethoxysilane,1H,1H,2H,2H-perfluorooctylmethyldimethoxysilane,1H,1H,2H,2H-perfluorooctyltrimethoxysilane,1H,1H,2H,2H-perfluorooctyldimethylchlorosilane,1H,1H,2H,2H-perfluorooctylmethyldichlorosilane,(1H,1H,2H,2H-perfluoro-n-hexyl)methyldichlorosilane,1H,1H,2H,2H-perfluorooctyltrichlorosilane, or combinations thereof. Theelectrolyte system 30 may include greater than or equal to about 0.1weight percent (wt %) to less than or equal to about 10 weight percent(wt %) of the one or more electrolyte additives.

Embodiments of the present technology are further illustrated throughthe following non-limiting examples.

EXAMPLE 1

FIG. 2 illustrates an electrolyte system 55 prepared in accordance withcertain aspects of the present disclosure. In particular, FIG. 2 showsan electrolyte system 55 comprising one or more salts bound to a solventto form a bound moiety. Electrolyte system 55 includes a bound moietycomprising lithium bis(fluorosulfonyl)imide (LiFSI) and dimethoxyethane(DME). Electrolyte system 55 includes a concentration of lithiumbis(fluorosulfonyl)imide (LiFSI) of about 5M and a molar ratio of thelithium bis(fluorosulfonyl)imide (LiFSI) to the dimethoxyethane (DME) ofgreater than or equal to about 1 to less than or equal to about 1.5.

As illustrated, substantially all of the dimethoxyethane (DME) moleculesbind with lithium (Li⁺). Thus, dimethoxyethane (DME) andbis(fluorosulfonyl)imide (FSI⁻) may be immobilized and the electrolytesystem 55 substantially free of free or unbound dimethoxyethane (DME)and free or unbound bis(fluorosulfonyl)imide (FSI⁻). Electrolyte system55 comprises less than or equal to about 0.5% by weight, optionally lessthan or equal to about 0.25% by weight, optionally less than or equal toabout 0.1% by weight, and in certain aspects, 0% by weight of the freeor unbound undesired species, free or unbound dimethoxyethane (DME) andfree or unbound bis(fluorosulfonyl)imide (FSI⁻). Thus, harmful sidereaction are eliminated or reduced thereby increasing the anodicstability of batteries including electrolyte system 55.

FIG. 3 illustrates a comparative electrolyte system 50 having a saltconcentration of less than about 4M. Electrolyte system 50 includes aconcentration of lithium bis(fluorosulfonyl)imide (LiFSI) of less thanabout 4M and a molar ratio of the lithium bis(fluorosulfonyl)imide(LiFSI) to the dimethoxyethane (DME) of about 0.4 (e.g.,LiFSI:DME=1:2.5). As shown, in such instances, a state of equilibriumexists between [Li⁺ (2 dimethoxyethane (DME))+freebis(fluorosulfonyl)imide (FSI⁻)] and [Li⁺ (dimethoxyethane(DME)+bis(fluorosulfonyl)imide (FSI⁻))+free dimethoxyethane (DME)]. Thefree or unbound bis(fluorosulfonyl)imide (FSI⁻) is highly reactive withlithium (Li) and may cause low lithium (Li) cycling efficiency (e.g.,about 98.4% efficiency). The free or unbound dimethoxyethane (DME) mayreact with high voltage (greater than about 4V) cathodes and may therebycause low full cell efficiency (e.g., less than about 99.5%). Moreparticularly, free dimethoxyethane (DME) may oxidized on one or moresurfaces of the cathode forming an internal redox species that can leadto low columbic efficiency.

Thus, providing electrolyte systems 55 with higher concentrations ofsalts can enhance anodic stability and provide the ability to use highervoltage cathodes by binding completely the one or more salts andsolvent. As seen in FIG. 4, the presence of the bound moiety inelectrolyte system 55 increases the ionization potential (eV) of theelectrolyte system 55 without increasing the electron the electronaffinity (eV). The y-axis or vertical-axis 60 of FIG. 4 depicts theelectron affinity (eV), while the x-axis or the horizontal-axis 70depicts the ionization potential (eV). Electrolyte system 55 includingthe bound moiety may have a calculated electron affinity of less than orequal to about 1.5 eV and a calculated ionization potential of greaterthan or equal to about 10 eV. While electrolyte system 50 not includinga bound moiety may have a calculated electron affinity of less than orequal to about 1.5 eV and a calculated ionization potential of less thanor equal to about 8 eV, and in certain instances, optionally less thanor equal to about 7.2 eV.

Resulting from the suppression or minimization of free or unbounddimethoxyethane (DME) and free or unbound bis(fluorosulfonyl)imide(FSL), a battery including electrolyte system 55 may include ahigh-voltage positive electrode. having a maximum potential greater thanor equal to about 4V, optionally greater than or equal to about 4.8V,and in certain aspects, optionally greater than or equal to about 5V.For example, the positive lithium-based electroactive material of thepositive electrode may be selected from the group consisting ofnickel-manganese-cobalt 811 (NMC811); nickel-manganese-cobalt 622(NMC622); lithium cobalt oxide (LiCoO₂); lithium iron phosphate(LiFePO₄); high-energy nickel-manganese-cobalt-oxide (HENMC) (e.g.,over-lithiated layered oxide cathode or lithium-rich NMC);lithium-manganese-nickel-oxide (LMNO); and combinations thereof.

EXAMPLE 2

FIG. 5 shows the charging and discharging profiles (e.g., cycle life) ofcomparative high-capacity 20 μm Li-NMC 622 electrochemical cells 100,200, and 300 including negative electrodes comprising metallic lithiumand varying electrolyte systems comprising lithiumbis(fluorosulfonyl)imide (LiFSI) and dimethoxyethane (DME). The y-axisor vertical-axis 80 depicts the capacity retention in milliamp hour(mAh), while the cycle number is shown on the x-axis 90. Electrochemicalcell 100 includes an electrolyte system prepared in accordance withcertain aspects of the present disclosure. In particular, theelectrolyte system of electrochemical cell 100 includes a bound moietyand has a lithium bis(fluorosulfonyl)imide (LiFSI) salt concentration ofabout 5M and a molar ratio the lithium bis(fluorosulfonyl)imide (LiFSI)to the dimethoxyethane (DME) of about 1. The electrolyte system ofelectrochemical cell 200 has a lithium bis(fluorosulfonyl)imide (LiFSI)salt concentration of about 4M, and the electrolyte system ofelectrochemical cell 300 has a lithium bis(fluorosulfonyl)imide (LiFSI)salt concentration of about 1.5M.

As seen electrochemical cell 100 has improved long term performance overelectrochemical cells 200 and 300. More particularly, electrochemicalcell 200 having a salt concentration of about 4M shows fast capacitydrop, while electrochemical cell 300 having a salt concentration ofabout 1.5M is unable to sustain a stable cycle. Accordingly,electrochemical cell 100 prepared in accordance with certain aspects ofthe present disclosure shows significant improved cycling performanceand reduced capacity fade. The electrolyte system of electrochemicalcell 100 is compatible with both negative electrodes (e.g., anodes)comprising metallic lithium and NMC cathodes.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. An electrochemical cell that cycles lithium-ionshaving improved or optimized capacity retention and anodic stabilitycomprising: a positive electrode comprising a positive lithium-basedelectroactive material selected from the group consisting ofnickel-manganese-cobalt 811 (NMC811), nickel-manganese-cobalt 622 (NMC622), and combinations thereof and having a maximum potential greaterthan or equal to about 5V; a separator; a negative electrode comprisinga negative electroactive material including lithium; and an electrolytesystem comprising a bound moiety having an ionization potential that isgreater than its electron affinity and an electrolyte additivecomprising 1H,1H,2H,2H-perfluorooctyltrimethoxysilane; wherein the boundmoiety comprises one or more salts bound to a solvent, wherein the oneor more salts is selected from the group consisting of: lithiumbis(fluorosulfonyl)imide (LiFSI), sodium bis(fluorosulfonyl)imide(NaFSI), potassium bis(fluorosulfonyl)imide (KFSI), and combinationsthereof and the solvent comprises dimethoxyethane (DME), wherein the oneor more salts have a concentration in the electrolyte system of greaterthan 5 M and a molar ratio of the one or more salts to thedimethoxyethane (DME) is greater than or equal to about 1 to less thanor equal to about 1.5, and wherein the electrolyte system issubstantially free of unbound dimethoxyethane (DME) and unboundbis(fluorosulfonyl)imide (FSI⁻).
 2. The electrochemical cell of claim 1,wherein the positive lithium-based electroactive material furtherincludes elemental sulfur or a sulfur-containing active material.
 3. Theelectrochemical cell of claim 1, wherein the positive lithium-basedelectroactive material further includes a material selected from thegroup consisting of lithium cobalt oxide (LiCoO₂); lithium ironphosphate (LiFePO₄); nickel-manganese-cobalt-oxide;lithium-manganese-nickel-oxide (LMNO); and combinations thereof.
 4. Theelectrochemical cell of claim 1, wherein the electrolyte system has adynamic viscosity of less than about 100 centipoise (cP), and theelectrochemical cell has an energy density of greater than about 900Wh/L.
 5. The electrochemical cell of claim 1, wherein the electrolytesystem includes one or more electrolyte additives selected from thegroup consisting of: 3,3,3-trifluoropropylmethyldimethoxysilane,(3,3,3-trifluoropropyl)trimethoxysilane,1H,1H,2H,2H-perfluorooctylmethyldimethoxysilane,1H,1H,2H,2H-perfluorooctyltrimethoxysilane,1H,1H,2H,2H-perfluorooctylmethyldichlorosilane,(1H,1H,2H,2H-perfluoro-n-hexyl)methyldichlorosilane,1H,1H,2H,2H-perfluorooctyltrichlorosilane, or combinations thereof.
 6. Amethod of preparing an electrolyte system that enhances or optimizescapacity retention and an anodic stability of an electrochemical cellcomprising a positive electrode comprising a positive lithium-basedelectroactive material selected from the group consisting ofnickel-manganese-cobalt 811 (NMC811), nickel-manganese-cobalt 622 (NMC622), and combinations thereof and having a maximum potential greaterthan or equal to about 5V and a negative electrode having a negativeelectroactive material comprising lithium, the method comprising: mixingone or more salts selected from the group consisting of: lithiumbis(fluorosulfonyl)imide (LiFSI), sodium bis(fluorosulfonyl)imide(NaFSI), potassium bis(fluorosulfonyl)imide (KFSI), and combinationsthereof; an electrolyte additive comprising1H,1H,2H,2H-perfluorooctyltrimethoxysilane; and a solvent comprisingdimethoxyethane (DME), wherein the one or more salts and the solventform a bound moiety having an ionization potential that is greater thanits electron affinity, wherein the electrolyte system is substantiallyfree of unbound dimethoxyethane (DME) and unboundbis(fluorosulfonyl)imide (FSI⁻), and wherein the one or more salts havea concentration in the electrolyte system of greater than 5 M and amolar ratio of the one or more salts to the dimethoxyethane (DME) isgreater than or equal to about 1 to less than or equal to about 1.5. 7.The method of claim 6, wherein the positive lithium-based electroactivematerial further includes elemental sulfur or a sulfur-containing activematerial.
 8. The method of claim 6, wherein the positive lithium-basedelectroactive material further includes a material selected from thegroup consisting of lithium cobalt oxide (LiCoO₂); lithium ironphosphate (LiFePO₄); nickel-manganese-cobalt-oxide;lithium-manganese-nickel-oxide (LMNO); and combinations thereof.
 9. Themethod of claim 6, wherein the electrolyte system has a dynamicviscosity of less than about 100 centipoise (cP), and theelectrochemical cell has an energy density of greater than about 900Wh/L.
 10. The method of claim 6, wherein the electrolyte additivefurther comprises one or more additives selected from the groupconsisting of: 3,3,3-trifluoropropylmethyldimethoxysilane,(3,3,3-trifluoropropyl)trimethoxysilane,1H,1H,2H,2H-perfluorooctylmethyldimethoxysilane,1H,1H,2H,2H-perfluorooctyldimethylchlorosilane,1H,1H,2H,2H-perfluorooctylmethyldichlorosilane,(1H,1H,2H,2H-perfluoro-n-hexyl)methyldichlorosilane,1H,1H,2H,2H-perfluorooctyltrichlorosilane, and combinations thereof.